The proposed research is concerned with the organization of DNA at the chromosomal level and in particular the structure of the ribosomal genes. We will seek to better understand the two phenomena which we have discovered in Drosophila melanogaster: ribosomal genes which appear not to be integrated into the DNA of the chromosome and supercoiled which differ between the DNA molecules carrying the ribosomal genes and the bulk of the DNA. Experiments involving sucrose gradient sedimentation, nucleic acid hybridization, and other techniques will be carried out to probe the structure of DNA in chromosomes and the special structures of ribosomal DNA. These studies have implications for the broader questions of how genes function and are regulated in normal and diseased states.